Which projection systems do Sentinel-1, -2 and -3 have?

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#1

Hello,

I am working with Sentinel-1, -2, -3 and Landsat 8 datasets, trying to combine them. Therefore I need to know which coordinate systems the datasets have and in case there are any differences, perform a reprojection.

I allready know, that Sentinel-1 (S1) and Sentinel-2 (S2) do not use the same projection. All I get from the metadata is, that S2 has a WGS84/UTM projection system and S1 has a geographic reference system, but it is not specified more. Landsat 8 (L8) also uses WGS84/UTM and in the metadata of Sentinel-3 (S3) I find epsg 4326.

Asuming that WGS84 is the datum for all these datasets (S1, S2, S3, L8), I only know the map projection for S2 and L8 (UTM). So I wonder which map projection S1 and S3 are using. Is it an ordinary geographic coordinate system (latitude, longitude)? For S1 data I can choose the map projection within the Range Doppler Terrain Correction in SNAP, so I think here it depends on my selection in SNAP?

Are the projections systems of S1 and S3 fully described with epsg 4326 (=Geographic Lat/Lon?) so I could use gdalwarp to convert S2 and L8 data? Would then all datasets have the same projection and coordinate system?

I might mix up some things, so I am happy for any explanation :slight_smile:

#2

Maybe some points for clarification:

  • Sentinel-1 is internally geocoded (coarse lat/lon coordinates), but not map projected. You have to select a projection in the range doppler terrain correction. As Sentinel- and Landsat are already UTM projected, I recommend selecting UTM as well
  • The term “WGS84” is ambiguous, because it refers to the geographic coordinate system (EPSG:4326) based on the WGS84 geoid and latitude and longitude coordinates. In combination with UTM projection (e.g. WGS84 / UTM Zone32N = EPSG:32632) it also specifies the underlying ellipsoid but UTM is a projected coordinate system with meters as unit.
  • Sentinel-3 is probably referenced to WGS84 (EPSG:4326) because it covers areas which overlap the UTM zones and the pixels are comparably coarse, so it is easier to store them as geographic coordinates (lat/lon).

So, whatever reference system you select, you have to reproject either Sentinel-3 or L8/S2. If the area is small (e.g. the extent of one S2 product), you are better off with the UTM zone (only reprojecting Sentinel-3). If you work at the global scale, having all data in WGS84 makes it easier. Lastly, you select the chosen reference for Sentinel-1 in the Terrain Correction step.

You can reproject with gdalwarp, but there is also a reprojection tool in SNAP.

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